Question

2 cos x = корень из 2

Answer 1

$2 cos x = sqrt{2}\ cos x = frac{sqrt{2}}{2} \x =pm arccosfrac{sqrt{2}}{2}} + 2pi n\\ x = pm frac{pi}{4} + 2pi n, n in mathbb{Z}$

Answer 2

$2cosx=sqrt2\cosx=frac{sqrt2}{2}\x=^+_-frac{pi}{4}+2pi n;nin Z$